STAT231: EXPERIMENTAL DESIGN

“EFFECTS OF STOCKING DENSITY AND SOURCE OF FORAGE FIBER ON SHORT-TERM RESPONSES IN RUMINAL FERMENTATION, BEHAVIOR, AND LACTATIONAL

PERFORMANCE OF HOLSTEIN DAIRY COWS”

Mac Campbell

Sam Kriegman

AIMS & OBJECTIVES Perform a analysis of stocking density/nutritional

interactions on: Ruminal environment (1°) Behavior (2°) Production (2°)

Measuring of this interaction is vital in: Maintaining optimal productive efficiency Well-being of cattle Providing data for nutritional models

EXPERIMENTAL DESIGN 2 x 2 factorial within a 4 x 4 Latin square design 14-day periods, with first 7 serving as adaptation period Multiparous (n=48) and primiparous (n=20) lactating Holstein cows Focal group of cannulated cows (n=16) Nuisances balanced for:

Days in Milk (190 ± 103)

Milk production (101 ± 18)

Parity (2.2 ± 1.1)

4 pens of cattle (n=17/pen) Experimental unit = pen Observational unit = cow

DETERMINATION OF TREATMENTSA) 100% Stocking Density, No Straw

B) 100% Stocking Density, Straw

C) 142% Stocking Density, No Straw

D) 142% Stocking Density, Straw

Example of the 2 x 2 Factorial within the 4 x 4 Latin square

PEN 10 PEN 11 PEN 12 PEN 13PERIOD 1 B C A DPERIOD 2 D A B CPERIOD 3 A D C BPERIOD 4 C B D A

MEASUREMENTS

Mean rumen pH H/d spent below pH 5.8

Continuous monitoring at 1-min intervals on d 12-14 of each period

Dry matter intake Average across d 8-14 of each period

Milk yield Average across d 8-14 of each period

Lying time Continuous monitoring at 10-min

intervals on d 8-10 of each period

EXPERIMENTAL MODEL (MIXED)

Yijklm = µ + Si + Dj + SDij + Pk + Rl + Eijklm

Where:

Yijkl = dependent variable

µ = overall mean

Si = fixed effect of stocking density

Dj = fixed effect of diet

SDij = fixed effect of the interaction between stocking density and diet

Pk = fixed effect of period

Rl = random effect of pen ~N(0, σ2r)

Eijklm = residual error, ~N(0, σ2e)

i = 1, 2 j = 1, 2 k = 1, 4 l = 1, 4 m = 1, 4

Pre-Planned orthogonal contrasts1. Low vs. High Stocking density2. Straw vs. No Straw Diet3. Interaction of stocking density and diet

POWER CALCULATIONS

Primary Objectives:

Secondary objectives

1. Krawczel et al. 20122. Yang and Beauchemin, 2007

r = 71 cows/pen r = 25 cows/pen

r = 50 cows/pen r = 33 cows/pen r = 15 cows/pen

RESULTS  100% 142%   P-value 

NS S NS S SEM STKD DIETSTKD

x DIET

Mean pH 6.17 6.13 6.09 6.10 0.03 0.07 0.62 0.39

pH < 5.8, h/d 2.29 1.90 4.12 2.77 0.41 <0.01 0.01 0.10

Intake, kg DM/cow

25.4 25.3 25.3 25.2 0.4 0.78 0.69 0.87

Lying Time, min/d 832 827 779 797 11 <0.01 0.56 0.31

Milk, kg/d 41.2 40.4 40.7 40.0 0.7 0.21 0.06 0.79

Significance at P ≤ 0.05Trends at 0.05 < P ≤ 0.10

LIMITATIONS

Experimental unit forced to be pen rather than individual cow

Loss of data during a single period forces the loss of entire cow from that particular measurement data set

OUTCOMES

Stocking density negatively affects lying time and ruminal pH

Straw diet counteracted the negative pH effect from higher stocking density with minimal affects on production and behavior